A holistic approach to central HVAC design for office buildings in Iran

Balancing thermal comfort, indoor air quality (IAQ), and energy use in office buildings located in cold semi-arid regions remains a major challenge, as most previous studies have examined these factors independently. This paper presents a replicable framework for the design and evaluation of a centralized HVAC system intended to replace conventional split-unit systems in a typical office building in Tehran. Dynamic energy simulation, computational fluid dynamics, and global sensitivity analysis are combined to assess thermal comfort, ventilation performance, and annual heating and cooling energy consumption. To provide a unified and holistic evaluation, this study introduces the Central HVAC Tri-Performance Index (CH-TPI), a composite decision-support indicator that integrates comfort (PMV, ULH), IAQ (LMA, ACE), and total HVAC energy use into a single normalized score. Results for Tehran show that the proposed HVAC system improves ventilation effectiveness and thermal comfort while lowering total HVAC energy consumption compared to the baseline case. Across the studied climates, Kerman and Isfahan achieve the highest CH-TPI values (0.803 and 0.794), matched by Shiraz (0.794) and followed by Tehran (PM) (0.756), while the baseline Tehran case shows the lowest performance (0.303). These findings highlight the effectiveness of the proposed framework and the importance of climate-responsive HVAC design.